1. Field of the Invention
The present invention relates to an exposure apparatus, and more particularly to a scanning projection exposure apparatus which performs exposure while moving a first object and a second object.
2. Related Background Art
Liquid crystal display panels are frequently used these days as a display device for word processors, personal computers, televisions, etc. A liquid crystal display panel is fabricated by patterning of transparent thin-film electrodes in a desired shape on a glass substrate by the photolithography technique. As an apparatus for the lithography a mirror projection type aligner is used for exposure-printing an original pattern formed on a mask onto a photoresist layer on a glass substrate through a projection optical system.
FIGS. 1 and 2 are drawings to show the structure of a conventional mirror projection type aligner. FIG. 1 is a perspective view to show the overall structure of the aligner and FIG. 2 is a lens cross-sectional view to show the structure of a projection optical system in the aligner.
In FIG. 1, an illumination optical system not shown illuminates a mask 71c in an arcuate illumination field 72a. An optical path of light from the illumination field 72a is deflected 90° by a First reflecting surface 73a of a trapezoid mirror 73, as shown in FIG. 2, and the thus deflected light advances via a concave mirror 74 and a convex mirror 75 and then is reflected again by the concave mirror 74. The optical path of the light reflected by the concave mirror 74 is deflected 90° by a second reflecting surface 73b of the trapezoid mirror. Then an image of the mask 71c or an image 72b of the illumination field 72a is formed on a plate 76.
The aligner as shown performs the so-called scanning exposure while moving the plate 76 and the mask 71c in the X direction in the drawings, whereby a circuit pattern on the mask 71c is transferred onto a selected region on the plate 76.
There is a recent demand to increase the size of liquid crystal display panels. With such a demand to increase the size, the above-described aligner is also desired to enlarge the exposure area.
In order to meet the demand to enlarge the exposure area, the conventional exposure apparatus as described above employed a method of exposure with exposure area as divided into pieces. Specifically, as shown in FIG. 1, an exposure area on the plate 76 is divided into four regions of 76a to 76d, and with scanning exposure of mask 71a and region 76a a circuit pattern of mask 71a is transferred onto the region 76a. In the next place, the mask 71a is exchanged for another mask 71b and the plate 76 is moved stepwise in the XY plane in FIG. 1 before a region 76b comes to coincide with the exposure area of the projection optical system. With scanning exposure of mask 71b and region 76b, a circuit pattern of mask 71b is then transferred onto the region 76b. After that, the same step is repeated for masks 71c and 71d and regions 76c and 76d, whereby circuit patterns of masks 71c and 71d are transferred onto corresponding regions 76c and 76d. 
In such exposure with divided exposure area, the multiple scanning exposure steps must be taken for a single exposure area, which decreases the throughput (an exposed substrate amount per unit time). Further, in case of the partition exposure, there are seams or stitches between two adjacent exposure regions and, therefore, the stitching accuracy must be enhanced. Because of this requirement, the method had such disadvantages that the magnification error of projection optical system must be decreased as close to as possible, that the alignment accuracy must be greatly improved, and that the production cost of the apparatus is increased.
On the other hand, it can be conceivable that the scale of projection optical system is increased for full scanning exposure of a single large exposure area instead of the partition exposure. In order to increase the scale of projection optical system, however, large-scale optical elements must be produced with very high accuracy, which results in increasing the production cost and the size of apparatus. Also, there was a disadvantage that the size increase of projection optical system caused an increase in aberrations or a decrease in imaging performance.